Ticks can cause direct injury as a result of their bites. The mouthparts of a tick are composed of two retractable hooked appendages that pull the skin over a single fixed harpoon-like structure that, itself, anchors the tick to the skin during feeding. These mouthparts are tiny, and enter just a fraction of a millimeter into the skin. By themselves, they rarely cause more damage then would a superficial splinter. You will not likely feel a tick walking on your skin. Furthermore, most tick bites neither are painful nor even noticeable (unless you happen to see the tick).
The tick produces copious saliva that it injects into the skin during feeding. This saliva contains a potent cocktail of substances that prevents blood clotting at the site and helps the tick feed. The tick’s saliva may cause diverse health effects on a person or animal. Generally, these effects are mild and are limited to local irritation and a bruise-like reaction around the bite site. With repeated exposure to tick bites, a person or pet may develop an allergic sensitivity to the saliva. This may cause the area around the bite to itch. Although this increases the extent of annoyance, the itching may cause the host to notice the tick and remove it before the tick causes yet greater risk. The saliva from a few kinds of ticks can cause a kind of paralysis that may begin at the lower extremities and proceed to sweep towards the head during a span of hours or days. This phenomenon, termed ‘tick paralysis’ is medically significant. It reverses rapidly once the causative tick has been located and removed. If allowed to proceed, however, tick paralysis can be fatal.